jakermc

I have a '83 SC with a '84 Euro engine (and lots of other engine mods) and I'm looking to add the factory chin spoiler and a tail to the body. Cosmetically, I like the look of the ducktail but I have a question about down force.

I know the bigger the tail, the bigger the down force, less oversteer, and less lift at high speeds. My question is how noticable is the difference between the ducktail and larger tails with regards to these characteristics? My second choice would probably be the RS America tail. I drive in DE events, not SCCA racing, and figure I would rarely get over 120 mph. The track I frequent the most keeps speeds under 110 mph. Should I worry about not having enough downforce with a smaller ducktail installed? Would performance be noticeably better with a bigger tail?

Bill Gregory

Paul Frere in his book "Porsche 911 Story" details the factory numbers on the effects each of the tails has. In order of increasing lift reduction: duck tail, Carrera tail, Turbo tail. The Turbo tail, due to it's shape, actually creates some downforce, as opposed to lift reduction. A tail starts to be effective around 60 mph and it's benefit goes up from there. I found a noticeable stabilizing benefit after I added a front valance (RUF) and Carrera tail (fiberglass) to my SC, at say around 110-120. Seemed a bit more stable at highway speeds, too.

Bill Verburg

Here are the aero charts from 'Panorama'

Cupcar

One thing, I think Bill Verburgs' graphs are for cars with a front spoiler, it's inadvisable to run without one.

I think the Carrera 3.2/RSA tail is slightly bigger than the "Turbo" tail in the graphs posted by Bill. If so it probably fits between the "Turbo" and "3.3 Turbo" curves above. Anybody know for sure? <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />

A930Rocket

How does the 3.8 RS tail fit in? I used to have one on my SC. I know it was goofy, but I liked it then and still do. I'm still toying with installing one on my 930.

Jim

Bill Verburg

The #s for the RS 3.8 tail are here
The tail in between the duck and 3.3 t is the original 76 930/tail. I always thought it was roughly the same as the 3.2 tail. But don't really know.

hoffman912

ok, i dont race and im not an expert, but this is at least what i got out of the article in 911 & porsche world number 88, july 01, in the article 'trick of the tail.' i hope this at least helps in some way. (if not get a back order and read the article, it is an excellent one!)

for the most stability it is best to have a wing, rather than a spoiler. the duck tail & whale tails are spoilers. what you see on an rs or gt2 or 3 is a wing. (or on indy, cart, f1 cars, le mans cars too)

example of a wing <img src="http://forums.pelicanparts.com/attachment.php?s=fe60a7a493586a25c528d3d45fc24514&postid=686889" alt=" - " />

a spoiler (such as ducktail, whale tail, tea tray etc etc) just "spoils" the air flow over the car, and 'can not create down force, other than as a biproduct of its intended purpose' . an actual wing, is exactly that a wing, but upside down. a wing (aerofoil) right side up (as in an air plane) causes lift. upside down it causes downforce (and is a direct product of its intended purpose).

why does porsche go for wings more than spoilers today? not because its more stylish.

btw.. you never run a wing or spoiler in the rear with out having one in the front! in order for one to be effective, you must have the other. it must all be balanced out. when they developed the front spoiler in the 67 911 s they found it helped stop front end lift, but worsened the controll probs with the rear. eventually they threw the duck tail on with the front spoiler, and gave the car far superior controll. one cannot work to its full potential with out the other and visa versa!

imho.. a duck tail looks great. it is the spoiler in its most original and purest form. however it is exactly that, original, old, extremely obsolete, and out of date as far as performance is concerned. unless its purpose is to be on a vintage car, or for soly a looks purpose, it is not worth it. on an 80s sc, either go with of date or better wings or spoilers for performance purposes. you will only notice it if you drive hard and fast enough to be able to notice it.

the article has way too much info to try to explain. it is as much a history lesson in porsches development of the tail as it is the and handling of them.

jakermc

Great stuff here - thanks to everyone.

Looking at the charts, it would appear that there isn't a whole lot of difference between the duck tail and the original whale tail/Carrera tails. If the charts are scaled correctly, the lift on the rear for the whale tail is about 5/6 the lift of the duck tail at 120 mph, or about 17 lbs. I'm not sure how noticeable this would be, even when driven hard on the track (at least at my modest level of ability). The significant jump comes from the 3.3 tail. Was this a wing?

Alan Herod

I suspect that the RS 3.8 wing/spoiler combination is that height because it is restricted by rules to some silouette. For a wing to be most effective it should be up in undisturbed air. I suspect that the lower the wing is, the higher the required angle of attack, which is somewhat undesirable in terms of drag. That is why it is so ironic (or moronic) to see an 89 automatic Honda Accord DX with a wing, nothing good will be accomplished.

Chris Picklo

Another thing to consider is the weight of these tails:

For example, would it be more beneficial to get a lighter fiberglass "turbo tail" as opposed to the OEM? Also, I know from experience the ducktail/lid combo is a lot lighter than a OEM turbo tail.

What are your thoughts on this?

Bill Verburg

Agreed. I saved 10#s by going to the lightest aftermarkt f/g tail that I could find.

The weight is saved in 2 of the better places to save chassis weight, high and aft.

The difference is noticeable

JackOlsen

Actually, there's a good argument for the ducktail being the best choice outside of a 3.8 RS tail. Look at the numbers: the ducktail adds very little weight (much less than the Carrera/Turbo tails), has about 5/6 the effectiveness of the later tails, and -- most importantly -- the other tails all increase the car's coefficient of drag, while the ducktail actually lowers it. A car with a ducktail will be faster in a straight line than one with any of the later tails, or even a car with no spoiler at all.

The ducktail was the engineers' first choice, and it was only eliminated because of German pedestrian safety regulations. The later tails reduced overall lift slightly better than the duck, but they did so at the expense of increased drag and increased weight. If horsepower hadn't been increased over the years, you'd see a lot of guys backdating to the ducktail and coming out ahead of the game.

As I understand it, the RS 3.8 tail was the first 911/930 tail that actually generated net downforce. All previous tails simply reduced lift.

I run an RS 3.8 tail on the track, and a duck on the street.

Chris Picklo

Does anyone know the difference in weight of a turbo tail + decklid and the ducktail?

Chris Picklo

Also, would PCA stock F class allow you to run with a duchtail?

Carrera51

Chris:
A ducktail in F stock would be OK.